Leukotrienes are a newly discovered class of arachidonic acid metabolites formed via the 5-lipoxygenase pathway in leukocytes and macrophages. These metabolites are potent biological agents and are involved in inflammatory reactions such as chemotaxis and immune responses such as anaphylaxis. We have recently observed that mouse spleen lymphocytes produce a leukotriene-like arachidonic acid metabolite, designated lymphocytic leukotriene (LLT). The chromatographic properties of this metabolite are different from those reported for leukotriene B4. Furthermore, the intriguing observation was made that LLT was a product of the 12-lipoxygenase metabolites. This project is designed to determine the chemical structure of this lymphocytic leukotriene, its mode of biosynthesis and its possible biological function. LLT will be isolated by HPLC and its structure determined by GC/MS. Mechanistic studies will be carried out to confirm preliminary observations that LLT is formed from arachidonic acid via two distinct pathways: 1. By the action of an 11,12-epoxidase on 12-HPETE and 2. By the sequential action of a 12- and a 5-lipoxygenase. In addition, we plan to subfractionate spleen cell populations into T- and B-lymphocytes and macrophages and determine the capacity of each cell type to product LLT. In preliminary experiments, it has been shown that inhibition of LLT formation by 15-HETE (a specific lipoxygenase inhibitor synthesized by leukocytes) is associated with loss of sensitivity to mitogenesis induced by the T-cell mitogen PHA but not the B-cell mitogen LPS. We will examine the chemotactic and chemokinetic activity of LLT towards neutrophils, the effect of LLT on T- and B-lymphocyte activation and modulation of cytotoxic effects of macrophages on tumor cells. The information obtained from these studies will assist in defining the role of lipoxygenase products as intercellular modulators of immunocompetent cells.